The present invention relates to a computer system and particularly relates to a data input-output control method used in the case where high throughput and high-speed response are required, and an apparatus using the method.
This type input-output controller (I/O controller) is generally disposed between a higher-rank apparatus such as a central processing unit and devices such as secondary storage devices represented by magnetic disk devices so that a chief object thereof is to perform I/O processing between the higher-rank apparatus and the devices asynchronously.
The I/O controller and the devices are connected by a single channel path or a plurality of channel paths, so that I/O commands and data are transferred through the channel paths between the I/O controller and the devices. The channel paths and the devices may be connected in one-to-one correspondence or one-to-multi correspondence or multi-to-one correspondence. The I/O controller can process a plurality of I/O requests simultaneously. In this situation, channel paths may be so busy that commands and data cannot be transferred even in the case where an I/O request is issued from the higher-rank apparatus. As a conventional measure to cope with the problem, an I/O device is described in Japanese Patent Unexamined Publication No. Sho-60-183660. In the I/O device, an I/O request queue is provided on a storage device connected to the I/O device so that an I/O request can be registered in the queue and that the I/O request can be picked up from the queue and processed when a target channel path is free.